The “Innovative Clean Transit” regulation will see the number of all-electric and hydrogen fuel cell buses purchased for public use in the state of California increase from 153 electric and fuel cell buses today to 1,000 by 2020.

Transit agencies will then follow a phase-in plan that will see the percentage of the 12,000-strong statewide fleet increase to 100% of all buses purchased by 2029.

The plan intends that the state transitions to exactly zero emissions from public bus fleets by 2040.

The plan will dramatically improve California’s poor air quality scorecard, reducing greenhouse gas emissions to the tune of 19 million metric tons from 2020-2050 – that is, the equivalent of 4 millions cars.

At the same time, CARB estimates that toxic nitrogen oxide emissions will be reduced by 7,000 tons and particulate matter pollution will be reduced by 40 tons.

While California has the highest percentage of privately-owned all-electric cars in the USA (50% of all registered EVs in fact), the planned increase of zero emissions buses will benefit the larger non-driving population as well as improve air quality as a whole.

CARB Chair Mary D. Nichols said in a statement that the rule in particular “dramatically reduces tailpipe pollution from buses in low-income communities and provides multiple benefits especially for transit-dependent riders.”

“Putting more zero-emission buses on our roads will also reduce energy consumption and greenhouse gases, and provides cost savings for transit agencies in the long run.”

The inclusion of public transport in clean air strategies is of particular importance not only because of the positive impact for city and urban centres but also in normalising alternative energy vehicles for the wider population.

California’s 200 off transit agencies will also benefit from greatly reduced maintenance and fuel costs, estimated by CARB at $US1.5billion ($A2.1billion) by the year 2050.